Objective: To study and evaluate root canal preparation using greater taper (GT) hand files in curved root canals. Material and Methods: Twenty-three teeth with 39 curved root canals in outpatients were instrumented with GT hand files, using the balance force technique, and obturated with standard gutta-percha points and a sealer (AHplus) using the lateral condensation method. Radiographs taken before, during, and after the operation were used to evaluate the efficiency of preparation and obturation. Results: In all cases the master apical GT hand files followed the course of the canal so that a continuously tapered root canal shape was achieved. No apical blockage or obvious aberrations were found. Only one file fractured during instrumentation. The mean preparation time for each curved canal was 9.75 ± 3.87 minutes. Good obturation was obtained in almost all cases. Conclusions: Under clinical conditions, the GT hand file prepared curved root canals effectively and safely, and the prepared canals possessed good taper and flow characteristics. The GT instrumentation technique is an efficient root canal preparation method for curved canals.